daitch_mokotoff module

Hello,

Please find attached a patch for the daitch_mokotoff module.

This implements the Daitch-Mokotoff Soundex System, as described in
https://www.avotaynu.com/soundex.htm

The module is used in production at Finance Norway.

In order to verify correctness, I have compared generated soundex codes
with corresponding results from the implementation by Stephen P. Morse
at https://stevemorse.org/census/soundex.html

Where soundex codes differ, the daitch_mokotoff module has been found
to be correct. The Morse implementation uses a few unofficial rules,
and also has an error in the handling of adjacent identical code
digits. Please see daitch_mokotoff.c for further references and
comments.

For reference, detailed instructions for soundex code comparison are
attached.

Best regards

Dag Lem